Editing Promethium (section)

==Properties==

===Physical properties===
A promethium atom has 61 electrons, arranged in the [[electron configuration|configuration]] &#91;[[xenon|Xe]]&#93;&nbsp;4f<sup>5</sup>&nbsp;6s<sup>2</sup>. The seven 4f and 6s electrons are [[valence electron|valence]] electrons.<ref name="Cotton">{{Greenwood&Earnshaw|page=1233}}</ref> In forming compounds, the atom loses its two outermost electrons and one 4f-electron, which belongs to an open subshell. The element's atomic radius is the second largest among all the lanthanides but is only slightly greater than those of the neighboring elements.<ref name="Cotton" /> It is the most notable exception to the general trend of the contraction of lanthanide atoms with the increase of their atomic numbers ([[lanthanide contraction]]<ref>{{Cotton&Wilkinson5th|pages=776, 955}}</ref>). Many properties of promethium rely on its position among lanthanides and are intermediate between those of neodymium and samarium. For example, the melting point, the first three ionization energies, and the hydration energy are greater than those of neodymium and lower than those of samarium;<ref name="Cotton" /> similarly, the estimate for the boiling point, ionic (Pm<sup>3+</sup>) radius, and standard heat of formation of monatomic gas are greater than those of samarium and less than those of neodymium.<ref name="Cotton" />

Promethium has a [[Close-packing of equal spheres|double hexagonal close packed]] (dhcp) structure and a hardness of 63&nbsp;kg/mm<sup>2</sup>.<ref name="str" /> This low-temperature alpha form converts into a beta, [[Cubic crystal system|body-centered cubic]] (bcc) phase upon heating to 890&nbsp;°C.<ref name="CRCrare" />

===Chemical properties and compounds===
[[File:Promethium(III) nitrate hydrate.jpg|thumb|150px|left|Promethium nitrate]]
[[File:Promethium-147 solution.jpg|thumb|150px|Solution containing Pm<sup>3+</sup> ions]]
Promethium belongs to the [[cerium group]] of lanthanides and is chemically very similar to the neighboring elements.{{sfn|Lavrukhina|Pozdnyakov|1966|p=120}} Because of its instability, chemical studies of promethium are incomplete. Even though a few compounds have been synthesized, they are not fully studied; in general, they tend to be pink or red in color.{{sfn|Emsley|2011|p=429}}<ref name="brit">[http://www.britannica.com/EBchecked/topic/478714/promethium promethium]. Encyclopædia Britannica Online</ref> In May 2024, a promethium coordination complex with neutral PyDGA ligands was characterized in aqueous solution.<ref>{{Cite journal |last1=Driscoll |first1=Darren M. |last2=White |first2=Frankie D. |last3=Pramanik |first3=Subhamay |last4=Einkauf |first4=Jeffrey D. |last5=Ravel |first5=Bruce |last6=Bykov |first6=Dmytro |last7=Roy |first7=Santanu |last8=Mayes |first8=Richard T. |last9=Delmau |first9=Lætitia H. |last10=Cary |first10=Samantha K. |last11=Dyke |first11=Thomas |last12=Miller |first12=April |last13=Silveira |first13=Matt |last14=VanCleve |first14=Shelley M. |last15=Davern |first15=Sandra M. |date=May 2024 |title=Observation of a promethium complex in solution |journal=Nature |language=en |volume=629 |issue=8013 |pages=819–823 |doi=10.1038/s41586-024-07267-6 |pmid=38778232 |issn=1476-4687|pmc=11111410 |bibcode=2024Natur.629..819D }}</ref> Treatment of acidic solutions containing {{chem2|Pm(3+)}} ions with [[ammonia]] results in a gelatinous light-brown sediment of hydroxide, [[Promethium hydroxide|{{chem2|Pm(OH)3}}]], which is insoluble in water.{{sfn|Lavrukhina|Pozdnyakov|1966|p=121}} When dissolved in [[hydrochloric acid]], a water-soluble yellow salt, [[Promethium(III) chloride|{{chem2|PmCl3}}]], is produced;{{sfn|Lavrukhina|Pozdnyakov|1966|p=121}} similarly, when dissolved in nitric acid, a nitrate results, [[Promethium(III) nitrate|{{chem2|Pm(NO3)3}}]]. The latter is also well-soluble; when dried, it forms pink crystals, similar to [[Neodymium(III) nitrate|{{chem2|Nd(NO3)3}}]].{{sfn|Lavrukhina|Pozdnyakov|1966|p=121}} The electron configuration for {{chem2|Pm(3+)}} is [Xe] 4f<sup>4</sup>, and the color of the ion is pink. The ground state term symbol is <sup>5</sup>I<sub>4</sub>.<ref>{{cite book|title=Chemistry of the f-block elements| author=Aspinall, H. C.|year= 2001| page=34, Table 2.1|publisher=Gordon & Breach|isbn=978-9056993337}}</ref> The sulfate is slightly soluble, like the other cerium group sulfates. Cell parameters have been calculated for its octahydrate; they lead to conclusion that the density of {{chem2|Pm2(SO4)3*8H2O}} is 2.86&nbsp;g/cm<sup>3</sup>.{{sfn|Lavrukhina|Pozdnyakov|1966|p=122}} The oxalate, {{chem2|Pm2(C2O4)3*10H2O}}, has the lowest solubility of all lanthanide oxalates.{{sfn|Lavrukhina|Pozdnyakov|1966|p=123}}

Unlike the nitrate, the [[promethium oxide|oxide]] is similar to the corresponding samarium salt and not the neodymium salt. As-synthesized, e.g. by heating the oxalate, it is a white or lavender-colored powder with disordered structure.{{sfn|Lavrukhina|Pozdnyakov|1966|p=121}} This powder crystallizes in a cubic lattice upon heating to 600&nbsp;°C. Further annealing at 800&nbsp;°C and then at 1750&nbsp;°C irreversibly transforms it to [[monoclinic]] and [[Hexagonal crystal system|hexagonal]] phases, respectively, and the last two phases can be interconverted by adjusting the annealing time and temperature.<ref name="PmO" />

{| Class = "wikitable" style = "text-align: center"
! Formula
! symmetry
! [[space group]]
! No
! [[Pearson symbol]]
! ''a'' (pm)
! ''b'' (pm)
! ''c'' (pm)
! ''Z''
! density, <br/>g/cm<sup>3</sup>
|-
| α-Pm
| [[Close-packing of equal spheres|dhcp]]<ref name="str">{{cite journal|doi=10.1016/0022-5088(71)90101-9|title=The crystal structure of promethium|year=1971|last1=Pallmer|first1=P. G.|last2=Chikalla|first2=T. D.|journal=Journal of the Less Common Metals|volume=24|issue=3|pages=233| issn = 0022-5088}}</ref><ref name="CRCrare">{{cite book |editor=Lide, D. R. |author=Gschneidner Jr., K.A. |chapter=Physical Properties of the rare earth metals |title=CRC Handbook of Chemistry and Physics |edition=86th |location=Boca Raton, FL |publisher=CRC Press |year=2005 |isbn=978-0-8493-0486-6 |chapter-url=http://203.158.253.140/media/e-Book/Engineer/Chemistry/Handbook%20of%20Chemistry%20and%20Physics/Section%2004/04_03_86.pdf |access-date=2012-06-20 |archive-url=https://www.webcitation.org/6AlZkPuDd?url=http://203.158.253.140/media/e-Book/Engineer/Chemistry/Handbook%20of%20Chemistry%20and%20Physics/Section%2004/04_03_86.pdf |archive-date=2012-09-18 |url-status=dead }}</ref>
| P6<sub>3</sub>/mmc
| 194
| hP4
| 365
| 365
| 1165
| 4
| 7.26
|-
| β-Pm
| [[Cubic crystal system|bcc]]<ref name="CRCrare" />
| Fm{{overline|3}}m
| 225
| cF4
| 410
| 410
| 410
| 4
| 6.99
|-
| Pm<sub>2</sub>O<sub>3</sub>
| cubic<ref name="PmO" />
| Ia{{overline|3}}
| 206
| cI80
| 1099
| 1099
| 1099
| 16
| 6.77
|-
| Pm<sub>2</sub>O<sub>3</sub>
| monoclinic<ref name="PmO">{{cite journal|doi=10.1111/j.1151-2916.1972.tb11329.x|title=Polymorphic Modifications of Pm2O3|year=1972|last1=Chikalla|first1=T. D.|last2=McNeilly|first2=C. E.|last3=Roberts|first3=F. P.|journal=Journal of the American Ceramic Society|volume=55|issue=8|pages=428}}</ref>
| C2/m
| 12
| mS30
| 1422
| 365
| 891
| 6
| 7.40
|-
| Pm<sub>2</sub>O<sub>3</sub>
| hexagonal<ref name="PmO" />
| P{{overline|3}}m1
| 164
| hP5
| 380.2
| 380.2
| 595.4
| 1
| 7.53
|}

Promethium forms only one stable oxidation state, +3, in the form of ions; this is in line with other lanthanides. Promethium can also form the +2 oxidation state.<ref>{{Holleman&Wiberg|page=1704}}</ref> Thermodynamic properties of Pm<sup>2+</sup> suggests that the dihalides are stable, similar to NdCl<sub>2</sub> and SmCl<sub>2</sub>.<ref>{{cite journal | last1=Elkina | first1=Veronika | last2=Kurushkin | first2=Mikhail | title=Promethium: To Strive, to Seek, to Find and Not to Yield | journal=Frontiers in Chemistry | volume=8 | date=2020-07-10 | page=588 | issn=2296-2646 | doi=10.3389/fchem.2020.00588 | doi-access=free| pmid=32754576 | pmc=7366832 | bibcode=2020FrCh....8..588E }}</ref>

{| Class = "wikitable" style = "text-align: center"
|+Promethium halides<ref>{{cite book|author=Cotton, Simon|title=Lanthanide And Actinide Chemistry|url=https://books.google.com/books?id=SvAbtU6XvzgC&pg=PA117|year= 2006|publisher=John Wiley & Sons|isbn=978-0-470-01006-8|page=117}}</ref>
! Formula
! color
! coordination<br/>number
! symmetry
! [[space group]]
! No
! [[Pearson symbol]]
! [[melting point|m.p.]] (°C)
|-
|PmF<sub>3</sub>
|Purple-pink
|11
|hexagonal
|P{{overline|3}}c1
|165
|hP24
|1338
|-
|PmCl<sub>3</sub>
|Lavender
|9
|hexagonal
|P6<sub>3</sub>/mc
|176
|hP8
|655
|-
|PmBr<sub>3</sub>
|Red
|8
|orthorhombic
|Cmcm
|63
|oS16
|624
|-
|α-PmI<sub>3</sub>
|Red
|8
|orthorhombic
|Cmcm
|63
|oS16
|α→β
|-
|β-PmI<sub>3</sub>
|Red
|6
|rhombohedral
|R{{overline|3}}
|148
|hR24
|695
|}

===Isotopes===
{{Main|Isotopes of promethium}}
Promethium is the only [[lanthanide]] and one of only two elements among the first 82 with no stable or long-lived ([[primordial isotope|primordial]]) isotopes. This is a result of a [[Isotopes of technetium#Stability of technetium isotopes|rarely occurring effect]] of the [[liquid drop model]] and stabilities of neighbor element isotopes; it is also the least stable element of the first 84.{{NUBASE2020|ref}} The primary decay products are [[neodymium]] and [[samarium]] isotopes (promethium-146 decays to both, the lighter isotopes generally to neodymium via [[positron decay]] and [[electron capture]], and the heavier isotopes to samarium via beta decay). Promethium [[nuclear isomer]]s may decay to other promethium isotopes and one isotope (<sup>145</sup>Pm) has a very rare alpha decay mode to stable [[praseodymium]]-141.{{NUBASE2020|ref}}

The most stable isotope of the element is promethium-145, which has a specific activity of {{convert|139|Ci/g|TBq/g|abbr=on|lk=on}} and a half-life of 17.7&nbsp;years via [[electron capture]].{{NUBASE2020|ref}}<ref name="CRCel" /> Because it has 84 neutrons (two more than 82, which is a [[magic number (physics)|magic number]] corresponding to a stable neutron configuration), it may emit an [[alpha particle]] (which has 2 neutrons) to form praseodymium-141 with 82 neutrons. Thus it is the only promethium isotope with an experimentally observed [[alpha decay]].{{sfn|Lavrukhina|Pozdnyakov|1966|p=114}} Its [[partial half-life]] for alpha decay is about 6.3{{e|9}}&nbsp;years, and the relative probability for a <sup>145</sup>Pm nucleus to decay in this way is 2.8{{e|-7}}&nbsp;%. Several other promethium isotopes such as <sup>144</sup>Pm, <sup>146</sup>Pm, and <sup>147</sup>Pm also have a positive energy release for alpha decay; their alpha decays are predicted to occur but have not been observed. In total, 41 isotopes of promethium are known, ranging from <sup>126</sup>Pm to <sup>166</sup>Pm.{{NUBASE2020|ref}}<ref name=Ln922>{{cite journal |last1=Kiss |first1=G. G. |last2=Vitéz-Sveiczer |first2=A. |last3=Saito |first3=Y. |display-authors=et al. |title=Measuring the β-decay properties of neutron-rich exotic Pm, Sm, Eu, and Gd isotopes to constrain the nucleosynthesis yields in the rare-earth region |journal=The Astrophysical Journal |volume=936 |issue=107 |date=2022 |page=107 |doi=10.3847/1538-4357/ac80fc|bibcode=2022ApJ...936..107K |s2cid=252108123 |hdl=2117/375253 |hdl-access=free |doi-access=free }}</ref>

The element also has 18 nuclear isomers, with [[mass number]]s of 133 to 142, 144, 148, 149, 152, and 154 (some mass numbers have more than one isomer). The most stable of them is promethium-148m, with a half-life of 43.1&nbsp;days; this is longer than the half-lives of the ground states of all promethium isotopes, except for promethium-143 to 147. In fact, promethium-148m has a longer half-life than its ground state, promethium-148.{{NUBASE2020|ref}}